Abstract

The exhibition of increasingly intensive and complex niche construction behaviors through time is a key feature of human evolution, culminating in the advanced capacity for ecosystem engineering exhibited by Homo sapiens. A crucial outcome of such behaviors has been the dramatic reshaping of the global biosphere, a transformation whose early origins are increasingly apparent from cumulative archaeological and paleoecological datasets. Such data suggest that, by the Late Pleistocene, humans had begun to engage in activities that have led to alterations in the distributions of a vast array of species across most, if not all, taxonomic groups. Changes to biodiversity have included extinctions, extirpations, and shifts in species composition, diversity, and community structure. We outline key examples of these changes, highlighting findings from the study of new datasets, like ancient DNA (aDNA), stable isotopes, and microfossils, as well as the application of new statistical and computational methods to datasets that have accumulated significantly in recent decades. We focus on four major phases that witnessed broad anthropogenic alterations to biodiversity—the Late Pleistocene global human expansion, the Neolithic spread of agriculture, the era of island colonization, and the emergence of early urbanized societies and commercial networks. Archaeological evidence documents millennia of anthropogenic transformations that have created novel ecosystems around the world. This record has implications for ecological and evolutionary research, conservation strategies, and the maintenance of ecosystem services, pointing to a significant need for broader cross-disciplinary engagement between archaeology and the biological and environmental sciences.

February 22, 2016

Accidentally or deliberately introduced species are the second most common threat associated with recent global extinctions of animals and plants, a new study from the University of Adelaide and UCL, in the UK, has found.

These ‘alien species’ have spread beyond their natural distributions by both deliberate and accidental human intervention since transnational shipping started in 1500AD─and many have significant negative environmental impacts.

The study published in the journal Biology Letters assessed how common alien species were listed as drivers of recent extinctions in plants, amphibians, reptiles, birds, mammals, using data from the IUCN Red List.

“Our results show that alien species are the second most common threat associated with species that have gone completely extinct from these groups since 1500AD,” says study leader Professor Tim Blackburn, Professor of Invasion Biology at UCL and Visiting Professorial Fellow at the University of Adelaide.

Alien species are just behind the most common threat averaged over all five groups ─ the most common being overexploitation of biological resources. They are, however, the most common threat associated with extinctions in each of three of the five groups analysed (amphibians, reptiles and mammals), and the most common threat when averaged over all the vertebrates (birds, amphibians, reptiles and mammals).

Across the globe, Australia has the highest rate of recent mammalian extinctions in the wild. Co-author Associate Professor Phill Cassey, Head of the University of Adelaide’s Invasion Ecology Group in the Environment Institute, says human activities were clearly raising extinction rates and the introduction of alien species is one of the leading causes.

“Many of these introductions have come through the legacy of European colonisation and the associated acclimatisation of animals and plants, which have become pests and weeds. However, with increased globalisation we now have a new suite of biological invaders: zoonotic diseases which because of airborne travel can arrive in the country in less than a day; and a large illegal biological trade in wildlife. This latter group is probably the least known, and therefore of considerable concern.

“The problem is that once these introduced species become established, eradication can be incredibly difficult. That is why we need such stringent biosecurity and to remain vigilant.”

In Australia, the “classic cases” of introduced mammalian species impacting biodiversity and causing extinctions are the generalist herbivores (rabbits, goats, pigs and camels) and the predators (feral cats and foxes).

“There have been a number of small to medium-sized Australian mammals now extinct because of these predators,” he says.

Was it humankind or climate change that caused the extinction of a considerable number of large mammals about the time of the last Ice Age? Researchers at Aarhus University have carried out the first global analysis of the extinction of the large animals, and the conclusion is clear — humans are to blame. A new study unequivocally points to humans as the cause of the mass extinction of large animals all over the world during the course of the last 100,000 years.

“Our results strongly underline the fact that human expansion throughout the world has meant an enormous loss of large animals,” says Postdoctoral Fellow Søren Faurby, Aarhus University.

Was it due to climate change?

For almost 50 years, scientists have been discussing what led to the mass extinction of large animals (also known as megafauna) during and immediately after the last Ice Age.

One of two leading theories states that the large animals became extinct as a result of climate change. There were significant climate changes, especially towards the end of the last Ice Age — just as there had been during previous Ice Ages — and this meant that many species no longer had the potential to find suitable habitats and they died out as a result. However, because the last Ice Age was just one in a long series of Ice Ages, it is puzzling that a corresponding extinction of large animals did not take place during the earlier ones.

Theory of overkill

The other theory concerning the extinction of the animals is ‘overkill’. Modern man spread from Africa to all parts of the world during the course of a little more than the last 100,000 years. In simple terms, the overkill hypothesis states that modern man exterminated many of the large animal species on arrival in the new continents. This was either because their populations could not withstand human hunting, or for indirect reasons such as the loss of their prey, which were also hunted by humans.

First global mapping

In their study, the researchers produced the first global analysis and relatively fine-grained mapping of all the large mammals (with a body weight of at least 10 kg) that existed during the period 132,000-1,000 years ago — the period during which the extinction in question took place. They were thus able to study the geographical variation in the percentage of large species that became extinct on a much finer scale than previously achieved.

The researchers found that a total of 177 species of large mammals disappeared during this period — a massive loss. Africa ‘only’ lost 18 species and Europe 19, while Asia lost 38 species, Australia and the surrounding area 26, North America 43 and South America a total of 62 species of large mammals.

The extinction of the large animals took place in virtually all climate zones and affected cold-adapted species such as woolly mammoths, temperate species such as forest elephants and giant deer, and tropical species such as giant cape buffalo and some giant sloths. It was observed on virtually every continent, although a particularly large number of animals became extinct in North and South America, where species including sabre-toothed cats, mastodons, giant sloths and giant armadillos disappeared, and in Australia, which lost animals such as giant kangaroos, giant wombats and marsupial lions. There were also fairly large losses in Europe and Asia, including a number of elephants, rhinoceroses and giant deer.

Weak climate effect

The results show that the correlation between climate change — i.e. the variation in temperature and precipitation between glacials and interglacials — and the loss of megafauna is weak, and can only be seen in one sub-region, namely Eurasia (Europe and Asia). “The significant loss of megafauna all over the world can therefore not be explained by climate change, even though it has definitely played a role as a driving force in changing the distribution of some species of animals. Reindeer and polar foxes were found in Central Europe during the Ice Age, for example, but they withdrew northwards as the climate became warmer,” says Postdoctoral Fellow Christopher Sandom, Aarhus University.

Extinction linked to humans

On the other hand, the results show a very strong correlation between the extinction and the history of human expansion. “We consistently find very large rates of extinction in areas where there had been no contact between wildlife and primitive human races, and which were suddenly confronted by fully developed modern humans (Homo sapiens). In general, at least 30% of the large species of animals disappeared from all such areas,” says Professor Jens-Christian Svenning, Aarhus University.

The researchers’ geographical analysis thereby points very strongly at humans as the cause of the loss of most of the large animals.

The results also draw a straight line from the prehistoric extinction of large animals via the historical regional or global extermination due to hunting (American bison, European bison, quagga, Eurasian wild horse or tarpan, and many others) to the current critical situation for a considerable number of large animals as a result of poaching and hunting (e.g. the rhino poaching epidemic).

New evidence gathered from sediments along the Delaware River in Pennsylvania is drastically revising theories about land use by Native Americans and the impact they once had on their environment. The new research reveals that from the period between 1100-1600 small agricultural settlements up and down the Delaware River Valley caused a 50-percent increase in sediment runoff into the Delaware River. This was done primarily by burn-clearing of as much as half of the forest-cover along the Delaware’s banks.

Conducted by scientists from the Smithsonian, the Center for American Archaeology, Baylor University and Temple University, the study shows that “Colonial-era Europeans were clearly not the first people to have an impact on the waterways in North America,” says archaeobiologist Timothy Messner of the Smithsonian’s National Museum of Natural History. “Widespread sedimentation caused by intensive settlement and maize farming in the Delaware Valley began about 500 years before European settlers arrived. And this was not just happening along the Delaware, but all over Eastern North America.” A paper on this subject was published recently in the scientific journal Geology.

[Image: Assorted kitchen knives on a magnetic strip.] I’m having trouble coping in a world that seems resigned to the inevitability of killing. Deliberate, premeditated killing. Whether of our “enemies” in other countries, “thugs” on our streets, or “livestock” on our farms, there always seem to be exceptions to the commandment that billions of people…